Process and apparatus for start-up of fiber-spinning solutions

ABSTRACT

A METHOD AND AN APPARATUS FOR THE START-UP OF A FIBER DRY SPINNING OPERATION WHEREIN THE SPINNING SOLUTION IS MAINTAINED AT A TEMPERATURE ABOVE THE BOILING POINT OF THE SOLVENT IN ORDER TO MAINTAIN A SPINNABLE SOLUTION. THE APPARATUS SEALS THE SPINNERET JETS TO PERMIT A BUILD-UP OF PRESSURE AND TEMPERATURE IN THE SPINNING SYSTEM TO THE REQUIRED SPINNING CONDITIONS WHILE PERMITTING SOLVENT BLEEDOFF TO PRODUCE A FLOW OF SPINNING SOLUTION INTO THE SPINNERET. SUBSEQUENTLY, THE SEALING MEANS IS DISENGAGED TO OPEN THE SPINNERET ORIFICE FOR SPINNING.

March 21, 1972 r. c. BOHRER 3,651,194

PROCESS AND APPARATUS FOR START-UP OP FIBER-SPINNING SOLUTIONS FIG.I

FIG.2

Filed Dec. 4, 196 8 Tlmnu C. Bohnr INVENTOR ATTORNEY United States Patent Ofice 3,651,194 Patented Mar. 21, 1972 3,651,194 PROCESS AND APPARATUS FOR START-UP OF FIBER-SPINNING SOLUTIONS Thomas C. Bohrer, Summit, N.J., assignor to Celanese Corporation, New York, NY. Filed Dec. 4, 1968, Ser. No. 781,030 Int. Cl. D01d 1/10, 7/00 US. Cl. 264-169 6 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The present invention relates to a device for placement onto spinnerets during start-up procedures in the spinning of shaped articles such as fibers and filaments. More particularly, the invention also relates to a method for building up the required pressure in a dry spinning system during startup of a spinneret without plugging the system or spinneret jets, such as may occur without the retention of sufficient pressure to reduce solvent losses at the temperatures required to obtain a freely flowable spinning solution.

The spinning of certain polymer solutions into shaped articles such as filaments is sometimes preferably eifected utilizing sol-vents which form polymer solutions only at temperatures above the solvent boiling point. In order to maintain solubility of the polymer in such solvents, elevated temperatures and superatmospheric pressures are maintained in the polymer solution. The start-up of spinnerette orifices utilizing such systems is extremely difficult because, unless sufficient pressure is maintained on the polymer solution, the solvent rapidly vaporizes at the solution temperature, thereby solidifying the polymer. In the start-up of such systems, considerable feed lines, spinneret manifolds, and the spinnerets themselves must be fed with the polymer solution while retaining it under sufficient pressure to inhibit solvent boiling and consequent solidification of the polymer. When a pressurized dope system is opened to the manifold and/or spinnerets without a pressurizing system such as described herein, the solvent rapidly evaporates from the polymer solution and escapes through the spinneret and filter means faster than the solution can be forced through the distribution system to the spinneret. The evaporation forms a hard polymer skin on the forward mass of polymer solution which subsequently blocks up solid against the filter and/or spinneret. Once the associated system, including the spinneret, is pressurized and filled with polymer solution, the back pressure from the orifices is normally sufiicient to enable retention of the polymer solution in the spinning system under the required pressure, thereby retaining the desired fluidity.

Examples of the type of spinning solutions to which the present invention is particularly applicable include, but are not limited to, the spinning of poly-4-methyl-1- pentene in percholoroethylene, polyphenyleneoxide in methylenechloride and methanol, high acrylonitrile polymers in acetonitrile or acetonitrile and water and the like spinning systems.

It is an object of the present invention to provide an apparatus which permits the maintenance of pressure in a spinning system while filling and bleeding polymer solutions through the spinneret on start-up, which apparatus can be subsequently disengaged to commence spinning operations. It is another object of the present invention to provide a method for maintaining pressure on a polymersolvent solution during the initial feeding of a spinning solution through the spinning system at temperatures above the boiling point of the solvent. These and other objects will become apparent to those skilled in the art from a description of the invention which follows.

In accordance with the invention, a method is provided for the start-up of a pressurized fiber-spinning system for a solution of an organic polymer in a solvent wherein said solution is maintained at a temperature above the boiling point of said solvent and said fibers are spun through an orifice from said solution while maintaining said solution under super-atmospheric pressure, the release of which pressure causes the rapid evaporation of said solvent and the solidification of said polymer, the improvement comprising pressure sealing said orifice, charging said spinning system with said solvent, increasing the temperature and pressure of said solvent to the fluid temperature of said polymer solution, passing polymer solution containing said solvent through said spinning system to replace the solvent with said polymer solution while maintaining said applied pressure and subsequently removing said vpressure seal from said orifice to commence the spinning of a tfiber.

In furtherance of the described method, a spinneret is provided, comprising a spinneret plate having an orifice therein and polymer feed means communicating with said plate and orifice, closure means for said orifice, said closure means comprising removable pressure sealing means, adopted for placement over said spinneret plate.

The present invention is particularly useful for the startup of spinning units ranging from single pilot plant units up to commercial spinning systems comprising several hundred or more spinnerets. The apparatus, described in its simplest form, can be operated manually or, as may be preferred for commercial production, automatically. For automatic operation, pressure release means can be provided to disengage the seal means for the commencement of the spinning operation at a predesignated pressure build-up; alternatively, mechanically, electrically, or other activation can be used as desired for the particular spinning operation. While the invention is preferably used in systems wherein the polymer-solvent provides a fluid solution only at temperatures above the boiling point of the solvent, the system can also be used to advantage in cellulose acetate and triacetate spinning start-ups, particularly when using spinnerets having a large number of orifices such as to 500 or more. The method permits charging of the spinnerets without cooling down the spinning dope.

DETAILS OF THE INVENTION The invention will be described more fully by reference to the drawing wherein:

FIG. 1 illustrates a sectional view of a dry spinning type spinneret and pressure sealing means according to the present invention adopted for manual removal of the orifice seal; and

FIG. 2 is a sectional view of a melt spinning type spinneret and pressure sealing means in accordance with the present invention.

The spinneret 10 comprises a spinneret plate 12 having one or more orifices or jets 14 therein. Communicating with the orifice is a chamber 30 which contains polymer solution during the spinning operation. Normally, positioning just above the spinneret plate 12 is a final filtering means 13 which for dry spinning is normally a fine mesh screen; and for melt spinning type spinnerets, sand and a breaker-plate is used. Spinneret can be specially constructed or conventional spinnerets can be modified as described herein.

Cover plate 16 is constructed to fit across the face of spinneret plate 12 and orifice 14 in a pressure sealing manner. Seal 18, which may be a rubber O ring, gasket or other pressure sealing means, is positioned in plate cover 16 in a manner whereby it engages the spinneret to form a gas tight seal over the spinneret plate. Plate cover 16 can be fitted into the sealing position over spinneret plate 12 in a number of ways. FIG. 1 illustrates a manual engagement whereby plate cover 16 is screwed onto coupling 22 attached to spinneret 10. Such manual engaged plate covers can be of the quick release type utilizing interrupted threads, whereby a one-eighth turn disengages plate cover 16 from spinneret 10.

Alternatively, as may often be desired, plate cover 16 can be automatically disengaged, such as by hinging cover plate 16 to spinneret 10 and locking it into place in the sealed position. A spring or other tension loaded means can be provided to swing cover plate 16 away from spinneret 12 and orifice 14 when disengaging on the start-up. The release can be pressure activated, electrically activated, manually activated or the like or predesignated pressure, electrical signal or the like.

Cover plate 16 preferably contains pressure release valve 20 through which solvent, air or entrapped vapors can be bled prior to the actual start-up of the spinning operation. Pressure release valve 20 is of a conventional type which is preset to a designated pressure. The preset pressure is normally that used in the actual spinning operation, but can be higher or lower provided the pressure used is sufficient to retain the solvent in liquid form in chamber 30. A typical pressure release valve 20 has vent passage 24 releasably blocked by spring loaded plunger 26. The presure setting is controlled by increasing or decreasing the tension on spring 28 by means of bolt 29.

In the start-up of a spinning operation utilizing temperatures above the boiling point of the solvents used to liquify the polymer to be spun, the spinning system is first filled or partially filled with the solvent used in the process.

The solvent used has a sufficiently high vapor pressure under the spinning or extruding conditions such that it rapidly flashes from the polymer, thereby rigidifying or gelling the polymer. Thus, the polymer rigidifies both be cause of the flashing of solvent and because of the lack of solubility at the reduced temperature. A typical solventpolymer system of this type is acetonitrile and acetonitrilewater combinations used with a high (85% or more) acrylonitrile fiber-forming polymer.

Having filled the spinning system through which the liquid polymer solution is passed with solvent from the dissolving and/or mixing zone to the spinning zone, the solvent is heated and pressurized to near the desired spinning temperature while maintaining the described pressure sealing plate covers in place over the spinnerets in a pressure sealing condition. For instance, when acetonitrilewater in a ratio of about 70 to 80 percent acetonitrile and about 20 to 30 percent water is used as a solvent for a high acrylic polymer such as those containing more than 85 percent acrylonitrile, the solvent is heated to a spinning temperature of about 120 degrees centigrade. This creates an autogenous pressure of about 40 to 50 pounds per square inch gauge which pressure is required to keep the solvent in the liquid state.

Polymer solution, also at an elevated temperature and pressure suflicient to maintain the polymer solution in a fluid condition, is then pumped through the spinning system to replace the solvent which was first added to the system. Pressure relief valve 20 is utilized to bleed the trapped solvent from the spinneret, thus this valve is set somewhat above the autogenous vapor pressure, such as 1 about 1 to 50 pounds or more above autogenous pressure, thereby allowing the spinning solution to fill the spinneret without plugging the orifice jets and/or filters in the spinneret and without evaporation of solvent within the system. When the spinning solution has substantially replaced the solvent and equilibrated in the system, the actual spinning process can then commence. Spinning is readily begun by removing cover plate 16 to permit the extrusion of filaments from spinneret 10.

The invention will be more fully described by reference to the following example which illustrates certain preferred embodiments of the present invention. Unless otherwise indicated, all temperatures are in degrees centigrade and all parts are by weight.

EXAMPLE A spinneret constructed in accordance with FIG. 1 was utilized in the spinning of acrylic filaments having an acrylonitrile content greater than percent. The acrylic polymer comprised about percent acrylontrile, 4.5 percent methyl methacrylate and 0.5 percent sodium methallyl sulfonate polymerized to inherent viscosity of about 1.4 as measured in 0.1 percent dimethyl formamide at 25 degrees centigrade. This polymer was solvated utilizing a solvent comprising about 80 percent acrylonitrile and 20 percent water. A solution of 41 percent acrylic polymer solids was prepared by mixing the solvent and polymer at a temperature of about 130 degrees centigrade and a pressure of about 50 pounds per square inch gauge. At this temperature and pressure, a homogeneous, free-flowing, spinning solution was formed. The release of the pressure on the solution rapidly solidified the polymer and flashed the solvent therefrom. Cooling of the solution,

even while maintaining pressure, also caused rapid formation of a gel.

The spinning system, which comprised feed lines running from the solvation zone to the spinneret, was then filled with the acetonitrile-water solvent. The solvent was heated to a temperature of about 120 degrees centigrade and a pressure of about 40 pounds per square inch gauge. The solvated polymer was then fed to the spinning system while releasing the added solvent to the atmosphere through the pressure release valve which was set for a pressure of about pounds.

The pressure release valve 20 could be preset to bleed off entrapped solvent at any desired pressure above the autogenous vapor pressure. Spinning of fibers was commenced by removing pressure plate 16. The back pressure created by the polymer contacting spinneret plate 12 was sufficient to ready maintenance of the desired pressure of about 40 pounds per square inch or more in the spining head thereby retaining the solvent and polymer solution in the liquid state in the spinneret. 'Fibers extruded from the spinneret were taken up by conventional dry spinning means.

While the invention has been described more particularly with respect to the spinning of high acrylonitrile fiber-forming polymers, it will be recognized that modacrylics and numerous other polymer-solvent combinations can be used without departing from the spirit of the present invention. However, because of the particularly unique characteristics of the more particularly described polymer-solvent systems, particularly the fact that the solvents only have the desired solvating characteristics at temperatures above their boiling points, such systems or combinations are used to the best advantage in the present invention. While there have been described various embodiments of the present invention, the methods and apparatuses described herein are not intended to be understood as limiting the scope of the invention as it is realized that changes therein are possible. It is intended that each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing substantially the same results in substantially the same or equivalent manner. It is intended to cover the invention broadly in whatever form its prin ciples may be utilized being limited only by the appended claims.

What is claimed is:

1. In a method for the start-up of a pressurized fiber spinning system for a solution of a fiber-forming organic polymer selected from the group consisting of acrylonitrile polymers, poly 4-methyl-1-pentene, polyphenylenoxide, cellulose acetate and cellulose triacetate, in a solvent wherein said solution is maintained at a temperature above the boiling point of said solvent and said fibers are spun through an orifice from said solution while maintaining said solution under superatmospheric pres sure, the inadvertent release of which pressure would cause the rapid evaporation of said solvent and the solidification of said polymer, the improvement comprising pressure-sealing said orifice, charging said spinning system with said solvent, increasing the temperature and pressure of said solvent to the fluid temperature of said polymer solution, passing polymer solution containing said solvent through said spinning system to replace the solvent with said polymer solution while maintaining said applied pressure while simultaneously dissipating the trapped solvent from said spinning system at a predetermined atmospheric pressure above the autogenous pressure applied to the solvent at the polymer temperature and allowing the polymer solution to fill said spinning system, and subsequenfly after said polymer solution has substantially replaced said solvent and equilibrated in said spinning system, removing said pressure seal from said orifice to commence the spinning of a fiber.

2. The method of claim 1 wherein the solvent produces a desired solvating effect only at temperatures above the boiling point of said solvent.

3. The method of claim 2 wherein the solvent is acetonitrile or mixtures of acetonitrile and water and the organic polymer is an acrylonitrile polymer of at least percent acrylonitrile.

4. The method of claim 1 wherein the polymer is solvated at a temperature above the boiling point of the solvent and at a pressure equal to at least the autogeneous pressure of said solvent at the solvatin temperature.

5. A spinneret comprising a spinneret plate having an orifice therein and polymer feed means communicating with said plate and orifice, closure means for said orifice, said closure means comprising pressure release means for the release of solvent at a predeterminable pressure and removable pressure sealing means adapted for placement over said spinneret plate.

6. The apparatus of claim 5 wherein the closure means are threaded for sealing engagement over said spinneret plate' by means of corresponding threads on said spinneret.

References Cited UNITED STATES PATENTS 2,330,932 10/1943 Taylor et a1. 264-169 2,872,702 2/1959 Dunlap et al 264169 3,461,193 8/1969 Gilandi 1812 1,671,878 5/1928 Topham 188 D 1,942,632 1/1934 Lowen 18-8 SS JAY H. WOO, Primary Examiner US. Cl. X.R.

l88 D, 8 SF; 134-22, 24, 166, 171; 264-39, 40, 85 204, 205 

